This project focuses on the outdoor resting and sugar-feeding behaviors of Anopheles malaria vector populations in Mali, West Africa, where, as in most African countries, malaria is a serious public health problem. An understanding of mosquito behaviors in the outdoor environment is becoming increasingly important because there is a growing awareness that vector control tools beyond those used exclusively inside houses are needed to achieve successful malaria control and local elimination. Currently, for the major malaria vector species in Africa, Anopheles gambiae, An. arabiensis, and An. funestus, there is only limited knowledge on their outdoor resting behavior, and the role of sugar or nectars in their life history is mostly speculated due to a lack of field-based evidence. Furthermore, resting and sugar feeding behaviors likely exhibit extensive phenotypic plasticity but the role of the ecological environment as the possible key driver has not been investigated. Therefore, the goal of this project is to investigate Anopheles mosquito outdoor resting and sugar- feeding behaviors at ecologically diverse sites in Mali to determine how complex relationships between these behaviors and the seasonally changing local environment affect malaria transmission. Field studies in Mali will be conducted at 10 study sites located in 3 major eco-climatic zones that span the sub-Saharan Sahel region. Study areas are already well characterized with respect to vector populations, seasonal Plasmodium falciparum transmission, and malaria epidemiology. This project, which builds on extensive preliminary studies in Mali and Israel, includes three specific aims: 1) Characterize how malaria vector species select from different types, configurations, and qualities of potential outdoor resting microhabitats and sugar-feeding centers, and behaviorally adapt to seasonal changes in their local environment~ 2) Determine how local environmental resources critical for malaria vector outdoor resting and sugar feeding affect malaria vectorial capacity and spatial aggregation patterns of malaria parasite transmission~ and 3) Develop and evaluate new approaches and field-based criteria to identify concentrations of adult anopheline mosquitoes in the outdoor environment. Innovative aspects include: First, new field-based approaches will be used to investigate two important but highly neglected mosquito behaviors, Second, this is the first study to examine how mosquitoes adapt their outdoor-resting and sugar-feeding behaviors in response to seasonal changes in their local environment. Third, this project will explain how outdoor-resting and sugar-feeding behaviors impact vector survival and malaria parasite transmission dynamics. Fourth, new predictive models for identifying concentrations of malaria vectors will be rigorously field-tested and refined to improve their accuracy and potential utility beyond Mali. By providing a strong scientific basis for development of new approaches and tools for anopheline mosquito vector control in outdoor environments, this project has strong potential for helping Mali and other countries improve malaria control and advance toward the ultimate goal of elimination.